Double beam progressive wave tube



SR D h K, to Jim July 31, 1956 H. HUBER ETAL DOUBLE BEAM PROGRESSIVEWAVE TUBE Filed May 25. 1950 VNJ I L EF I IT a J 1 LI a LuLv q Lv

United States Patent DOUBLE BEAM PROGRESSIVE WAVE TUBE Harry Huber,Paris, France, and Werner Kleen, Madrid, Spain, assignors to CompagnieGenerale dc Telegraphic Sans Fil, a corporation of France ApplicationMay 25, 1950, Serial No. 164,127

Claims priority, application France June 2, 1949 6 Claims. (Cl. 315-35)The present invention relates to a particular form of travelling wavetube and to the application of this tube to arrangements in which thisform affords considerable advantages.

It is well known that the operation of a travelling wave tube is basedon the phenomenon of interaction between an electron beam and atravelling wave, this wave being amplified by this interaction efiect ifthe speed of the electrons is approximately equal to the phase velocityof the wave. The invention relates to this type of tube, and moreparticularly both to those in which the interaction space is notsubjected to the action of a transverse electrostatic field or to theaction of a transverse magnetic field (Kompfner-Pierce type), and totubes having crossed electrostatic and magnetic fields, as proposed inapplication Serial No. 794,164, filed on December 27, 1947, now PatentNo. 2,511,407, and in application Serial No. 102,896, filed on July 2,1949, now Patent No. 2,687,777.

The tube according to the invention is characterised by the existence oftwo electron beams propagated in opposite directions, the two beamsmoving in the electromagnetic field of waves guided by a same delayline. However, there is only one delay line defining two electron andwave interaction spaces, each of which is traversed by one of the twoelectron beams.

The accompanying drawings illustrate two examples of the invention asapplied to travelling Wave tubes respectively without and with atransverse magnetic field.

In these drawings, Figure 1 is an axial section of a first embodiment oftube without a transverse magnetic field, and Figures 2 and 3 arerespectively an axial section, and a cross-section on line 33 of Figure2, of a second embodiment with a transverse magnetic field.

With reference to Figure 1, the tube has, at one of its ends, anelectron gun generating a tubular beam 1 which is propagated along theoutside of a linear helix 2 employed as a delay line. The gun iscomposed of the annular cathode 3, the Wehnelt or control cylinder 4 andthe accelerating or anode electrode 5. At the opposite end is situatedanother electron gun constituted by a cirular cathode 6, the Wehneltcylinder 7 and the anode 8. This gun generates the second beam ofelectrons 9, which is propagated along the inside of the helix 2 in theopposite direction to the beam 1. At the two ends of the helix aresituated dipoles 10 and 11 providing the coupling between the delay line(helix) and the wave guides 12 and 13. The tube is surrounded by amagnetic coil 14 serving to focus the beams. A battery 24 is providedfor each gun with a connection from its positive terminal to the anodeor 8 and a potentiometer 25 across its two terminals and connected byintermediate taps 26 and 27 to the cathode 3 or 6 and to the controlcylinder 4 or 7. For control purposes, each control electrode 4 or 7 mayhave a control circuit 28 connected thereto.

The advantage of the tube operating with two beams propagated inopposite directions, as compared with a tube operating with one beamonly, will be obvious on ex- 2,757,311 Patented July 31, 1956 planationof the operation of the tube according to the invention. There are inparticular two possible advantageous applications:

(a) One of the two beams serves to amplify an injected wave, while theother generates an internal feedback which causes the amplification toincrease.

(b) The tube serves for amplification in both directions, it beingpossible to discontinue the amplification in one of the directions whenthe amplification in the other direction takes place.

In order to explain the application referred to under (a), it will beassumed by way of example that the signal to be amplified is introducedby means of the guide 12. The amplification is then efiected by means ofthe tubular beam 1, the mechanism of this amplification being wellknown, so that it is unnecessary to describe it in detail. The wave tobe amplified is propagated in the direction toward the guide 13 and thefield of this wave has practically no influence on the behaviour of thesecond beam, except at the output end, that is to say, in the region ofthe guide 13. If a small error in matching is left between the guide 13and the dipole 11, a standing wave is produced which excites a wavemoving in the opposite direction to the wave introduced by means of theguide 12. This second wave, which moves in the direction of the beam 9,generated by the cathode 6, is amplified owing to the interaction withthis beam. If a small error in matching is left between the guide 12 andthe dipole 10 a new standing wave is produced at this point on arrivalin the guide 12. On suitable adjustment of the phase of this secondwave, an increase of the input signal is obtained, that is to say, theprocess corresponds to an internal feedback which causes the gain of thetube to increase. The adjustment of the phase may be effected byregulating the potential of the cathode 3 with respect to that of thehelix 2 and the feedback mechanism may be regulated by variation of thepotential of the second cathode 6 or by regulation of the current of thebeam 9 serving as a reaction element.

The application referred to under (b) is advantageous, for example, in aradiotelephonic connection on a carrier wave in the centimetric waverange. In this case, the tube permits amplication in both directions andthe signal can be introduced either into 12 or into 13, it beingpossible to tap the amplified power either by means of 13 or by means of12. For this application of the tube, it may be desirable to suppressthe feedback. This is done by interrupting the current of the beam whosedirection is opposite to the desired direction of amplification, bynegative impulses supplied by the control circuit 28 of one of theWehnelt cylinders, for example. The natural attenuation of the helix issufiiciently great for a signal, which is not amplified by theinteraction with the beam, to be sufliciently attenuated. The means forthe automatic suppression of one of the directions of amplification andcommutation of the latter are well known in the art of line telephony,and although they may also be applied (as shown) in the circuit of thistube they are not included in the invention.

It is possible that the tube operating with two beams propagated inopposite directions may be more difiicult and more costly to constructthan two tubes operating with a single beam, each of which serving foramplification in one direction only. However, the use of the tubeaccording to the invention makes it possible to employ the same externalcircuits for amplification in the two opposite directions, while twotubes operating with a single beam require separate circuits.

The principle of the invention is not limited to a tube of the typeshown in Figure 1, in which the magnetic field serves for focussing andis directed in the direction of propagation of the waves. It may also beapplied to a tube having crossed magnetic and electrostatic fields, themechanism of which has been described in the specifications hereinbeforereferred to. A tube of this nature is shown in Figures 2 and 3. Thereferences 3 and 6 designate the two cathodes. The delay line consistsof a flat helix 2 or of a wire bent in sinuous form, which is situatedbetween two conductors 22 and 23. The two interaction spaces aresituated on either side of the helix. In order to generate thetransverse electric field necessary for the operation of this type oftube, the two conductors 22 and 23 are negative with respect to thehelix 2. The transverse magnetic field in Figure 2 is perpendicular withrespect to the plane of the drawings. In Figure 3, and 17 indicatediagrammatically the pole pieces of the magnet generating this magneticfield.

Instead of guides 12 and 13 as shown in Figure 1, there are employed inthe tube shown in Figure 2, by way of example, coaxial lines coupled tothe two extremities of the helix 2, one of which, 16, is shown in Figure3.

As in the tube shown in Figure 1, the two beams leaving the cathodes 3and 6 have opposite directions and are propagated in the field of thesame delay line. The transverse magnetic field has the same direction inboth in teraction spaces, and the two electrostatic fields musttherefore be of opposite direction in order that the movements of theelectrons may be opposed.

The principle of the invention is not limited to tubes with a helix or asinuous Wire employed as the delay line, but may be applied to tubeshaving a delay line of any form, the applications of the principle inthe tubes shown in Figures 1 and 2 only being shown by way of example.

Similarly, the principle is not limited to tubes of linear form, but isalso applicable to tubes of circular form.

We claim:

1. An electron discharge tube comprising an envelope, a delay linedividing the inside of the envelope into two distinct separate parallelelectron and wave interaction ducts, ultra-high frequency terminalscoupled to opposite nections to the line and sources for biasing thelatter negatively with respect to the former, and means associated witheach source for concentrating the emission thereof into a beampropagating in the associated duct at a desired velocity substantiallyequal to the wave phase velocity of energy flowing in the line in thesame direction.

2. An electron discharge tube comprising a retardation line in the formof a helix, means coupled with one end of said line for introducingultra-high frequency energy into said line, means coupled with the otherend of said line for extracting the amplified ultra-high frequencyenergy, means comprising an emissive cathode situated near one end ofsaid retardation line and a source of potential connected between saidcathode and said line for giving to said cathode a negative potentialwith respect to said line, and a system of electron lens electrodes,with accelerating and focusing means for causing the electronsconcentrated in tubular beam form to enter an interaction space adjacentand exterior to said line, and parallel thereto, at a velocitysubstantially equal to the phase velocity of the ultra-high frequencyenergy introduced in said one end of the line and propagating towardssaid other end thereof, means for causing propagation of ultra-highfrequency en ergy from said other end towards said one end of the line,and means comprising a second emissive cathode situated near said otherend of said line with a second system of electron lens electrodes andaccelerating and focusing means, and a source of potential connectedbetween said second cathode and said line for giving to said secondcathode a negative potential with respect to said line thereby to directa beam of electrons of cylindrical form, inside said helix, in theopposite direction to and uncoupled from the beam of said first cathode,at a velocity substantially equal to the phase velocity of theultra-high frequency energy propagating in opposite direction withrespect to said energy introduced in the line.

3. An electrondischarge tube, comprising a retardation line, meanscoupled with one end of said retardation line for introducing ultra-highfrequency energy, on one side of said line a first emissive cathodesituated near one end of said line and emitting a first electron'beamand a first conducting electrode extending parallel to said retardationline, on the other side of said line, a second emissive cathode locatednear. the other end of said line and emitting a second electron beamuncoupled from said first beam, and'a second conducting electrodeextending parallel to said line and to said first electrode, said lineand said electrodes defining therebetween two interaction spacesseparated by said line, means comprising a source of potential connectedto said line on one hand, and to said cathodes and said electrodes onthe other hand, for giving negative potentials to said cathodes and saidelectrodes with respect to said line, and means for establishing asubstantially time constant magnetic field in said interaction spacessubstantially perpendicular to said line and parallel to saidelectrodes, thereby to direct two parallel and reciprocally offsetelectron beams into said interaction spaces, said beams travelling inreciprocally opposite directions at a velocity substantially equal tothe phase velocity respectivcly of the ultra-hi h frequency energyintroduced in said one end of the line and propagating towards saidother end, and of the ultra-high frequency energy propagating oppositeto the former.

4. A tube as claimed in claim 1 in combination with means for varyingthe potentials of the two sources.

5. A tube as claimed in claim 1 in combination with means for varyingthe current of at least one of the two electron beams.

6. A tube as claimed in claim 1 in combination with means for applying avoltage to an electron lens electrode to interrupt the current of one ofthe beams.

References Cited in the file of this patent UNITED STATES PATENTS2,280,824 Hansen et al. Apr. 28, 1942 2,381,320 Tawney Aug. 28, 19422,406,370 Hansen et al. Aug. 27, 1946 2,406,371 Hansen et al. Aug. 27,1946 2,479,084 Rosenthal Aug. 16, 1949 2,511,407 Kleen et al June 13,1950 2,578,434 Lindenblad Dec. 11, 1951 2,585,582 Pierce Feb. 12, 19522,600,509 Lerbs June 17, 1952 2,607,904 Lerbs Aug. 19, 1952 2,635,206Pierce Apr. 14, 1953 2,652,513 Hollenberg Sept. 15, 1953 OTHERREFERENCES Article by A. V. Hollenberg, pp. 52-58, Bell System Tech.Journal for January 1949.

Article by A. V. Haefi, pp. 4-10 incl., Proc. I. R E. for January 1949.

